The invention relates to a process and apparatus for the nitric oxide-free combustion of liquid and gaseous fuels, wherein fuel gases such as natural gas, liquefied gas, or heating oil are burned in such a way that no nitric oxides are formed.
In gas and oil combustion plants, the fuels are commonly burned in a flame which, at least locally, has temperatures far exceeding 1300.degree. C., which means that nitric oxides are produced. Furthermore, complete combustion requires an excess of air, which prevents the relatively complete utilization of the liberated heat.
Efforts to achieve nitric oxide-free fuel combustion have been made by dividing the combustion into stages in such a way that the formation of nitric oxides in the exhaust gas is reliably prevented. For this purpose, the reaction of the fuel with the air has to take place in all phases of the controlled reaction in such a way that the liberation of heat by combustion reactions and the subsequent cooling of the flue gas take place within a temperature range below 1300.degree. C. or under a reducing atmosphere, or with the reduction of any resulting nitric oxides in a reducing atmosphere by catalytic action.
Efforts to achieve the objective of nitric oxide-free combustion by dividing the reaction into a gasification reaction with partial catalytic oxidation and subsequent cooling of the resulting fuel gas, and combustion of the gasification gas in a second stage, were not successful. The desired objective was not obtained because the hot flame, having a temperature of 1800.degree. C., was not divided into two partial zones of 900.degree. C. This result was due to the intermediate cooling of the gasification gas, which led only to the dissipation of a lower amount of heat, because the volume of the gasification gas represents only a portion of the end or final volume. Thus, significantly higher temperatures were produced in the second stage, which limited the life or durability of the catalysts, and led to the formation of nitric oxide due to overheating, though only to a minor extent. In addition, this created ignition problems in the combustion plant because higher ignition energies for starting the equipment are required under the given conditions of a reducing atmosphere.
Accordingly, it is an object of the present invention to provide a method and apparatus which avoids the above-identified obstacles and achieves combustion of liquid or gaseous fuels, with exhaust gases which are completely nitric oxide-free.
It is also an object of the invention to provide such a method and apparatus which also has a very good utilization efficiency of the combustion heat of the fuel.